f check for required features

Author: valentinewallace

lightning/src/blinded_path/mod.rs

@@ -86,6 +86,7 @@ impl BlindedPath {
 	/// * [`BlindedPayInfo`] calculation results in an integer overflow
 	/// * the list of [`BlindedPaymentTlvs`] does not consist of 0 or more
 	///   `BlindedPaymentTlvs::Forward` followed by 1 `BlindedPaymentTlvs::Receive`
+	/// * any unknown features are required in the provided [`BlindedPaymentTlvs`]
 	//  TODO: make all payloads the same size with padding + add dummy hops
 	pub fn new_for_payment<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>(
 		path: &[(PublicKey, BlindedPaymentTlvs)], entropy_source: &ES, secp_ctx: &Secp256k1<T>

lightning/src/blinded_path/payment.rs

@@ -68,6 +68,12 @@ impl BlindedPaymentTlvs {
 				payment_constraints.htlc_minimum_msat,
 		}
 	}
+	fn features(&self) -> Option<&BlindedHopFeatures> {
+		match self {
+			Self::Forward { features, .. } => Some(&features),
+			Self::Receive { .. } => None,
+		}
+	}
 }
 
 /// Parameters for relaying over a given [`BlindedHop`].
@@ -167,6 +173,10 @@ pub(super) fn compute_payinfo(
 	let mut curr_base_fee: u32 = 0;
 	let mut curr_prop_mil: u32 = 0;
 	for (_, payment_tlvs) in path.iter().rev().skip(1) {
+		// In the future, we'll want to take the intersection of all supported features for the
+		// `BlindedPayInfo`, but there are no features in that context right now.
+		if payment_tlvs.features().map_or(false, |f| f.requires_unknown_bits()) { return Err(()) }
+
 		let next_base_fee = payment_tlvs.fee_base_msat();
 		let next_prop_mil = payment_tlvs.fee_proportional_millionths();
 		// Use integer arithmetic to compute `ceil(a/b)` as `(a+b-1)/b`
@@ -193,7 +203,6 @@ pub(super) fn compute_payinfo(
 		htlc_minimum_msat: path.iter().map(|(_, tlvs)| tlvs.htlc_minimum_msat()).max().unwrap_or(0),
 		// TODO: this field isn't present in route blinding encrypted data
 		htlc_maximum_msat: 21_000_000 * 100_000_000 * 1_000, // Total bitcoin supply
-		// TODO: when there are blinded hop features, take the intersection of them here
 		features: BlindedHopFeatures::empty(),
 	})
 }